It is known to provide pumping systems for use in mobile applications such as vehicle-mounted pumping systems. An example of one such system is disclosed in U.S. Pat. No. 6,551,073 B1 (O'Sullivan) which discloses a pumping system typically used on a fire truck. In this application, the vehicle is provided with a hydraulic drive system wherein a liquid pump for pumping water is driven by a fixed displacement hydraulic motor, which motor is in turn driven by a variable displacement hydraulic pump. A controller is provided to modulate hydraulic output of the variable displacement hydraulic pump to maintain a constant liquid pressure at the outlet of the water pump. The system uses an electronic control system comprising a motor speed transducer for the hydraulic motor and a liquid outlet pressure transducer, which transducers are connected to an electronic controller device that thereby varies the output of the variable displacement hydraulic pump to vary the liquid pressure and control the motor speed. However, the system may be undesirable since fluctuations in the liquid outlet pressure may occur which may make it difficult to quickly make corresponding changes in the variable displacement hydraulic pump. Further, the electronic control system may be subject to failure, particularly in hostile environments wherein an electronic control system may be difficult to maintain.
It is an object of the invention to provide an improved pumping system for mobile applications, particularly where a pumping system is provided on vehicles such as a trailer or the like. Further, it is an object of the invention to provide a pumping system which provides an improved control of the liquid outlet pressure supplied by a fluid pump, and provide a system which is particularly suitable for hostile environments which require a stable drive system for the pumps as well as a control system therefor.
The pumping system of the invention is a mobile, vehicle-mounted pumping system, such as for water, fuels or other suitable liquids, which mounts on a trailer and may be used for various applications where it is necessary to pump fluids, such as a variety of liquids from remote and/or temporary storage tanks and facilities. While the following summary may reference liquid pumps for convenience, any of a variety of process fluids may be pumped or distributed by fluid distribution equipment. The system comprises one or more fluid or liquid pumps which are connected to and driven by a drive system for the pumps and by a control system for controlling the outlet pressure of the liquid or process fluid being discharged from the pumps.
The pumping system operates the drive system and the control system almost exclusively by hydraulic fluid pressure which avoids the necessity of an electronic control system to control the pump outlet pressure which may be more complex to maintain and susceptible to failure, particularly in harsh, hostile or remote environments.
The main system components are a diesel engine, one or more fluid pumps for distributing the process fluid, which pumps preferably are each driven by a hydraulic motor, a hydraulic drive system, which generates hydraulic fluid pressure to drive each motor, and a hydraulic control system, which controls and varies the output of the process fluid pressure of the liquid pumps by varying the pressure of the hydraulic fluid that drives each hydraulic motor. The process fluid pumps preferably are positive displacement pumps which pump liquids as the process fluid.
To generate the hydraulic system pressure, a drive shaft of the diesel engine is connected to and drives a variable displacement hydraulic pump, i.e. a main pump, wherein the pump output is the system pressure that is supplied to and drives the hydraulic motors. The main pump has a variable output that selectively varies the system pressure generated thereby to thereby vary the motor operation which in turn, varies the pump output from the fluid pumps. The pumping system operates upon the principal that the system pressure driving the motors directly corresponds to or is proportional to the liquid output pressure in the fluid distribution system. For example, 5200 psi of hydraulic system pressure supplied to the hydraulic motor generates an outlet pressure from the liquid pump of 150 psi. A controlled reduction in the system pressure correspondingly reduces the fluid pump outlet pressure such that controlling the hydraulic system pressure driving the motors also controls the fluid pressure that is output from the pumps.
The output of the main pump is controlled mechanically by a swash plate wherein the position of the swash plate is selectively moved to vary the pump displacement and outlet pressure generated by the main pump when driven by the diesel engine. Preferably, the output of the main pump is accomplished by destroking the main pump. The invention comprises the method and system for moving the swash plate to control the system pressure and thereby control the fluid pump output and vary the liquid output pressure supplied to the distribution system.
The swash plate is mechanically moved by a swash plate control which is a pressure balancing solenoid that is pressurized on one side by a low charge pressure supplied by a charge pump which charge pump is also driven by the diesel engine. The pressure balancing solenoid is pressurized on a second side by a variable control pressure which preferably is a destroking pressure that destrokes the main pump to vary its output. This control pressure is manually adjustable by a system control valve to set the maximum system pressure and maintain such pressure. This system control valve receives the high system pressure from the outlet of the main pump and has a manually rotatable valve wherein a control knob is rotated to set the max system pressure. In this regard, the control valve is adjusted which essentially generates an adjusted pressure exiting the control valve which is fed to the swash plate control solenoid as the destroke pressure to vary the swash plate in a manner that quickly varies the system pressure that is output from the main pump in correspondence to the adjusted destroke pressure supplied to the solenoid.
Initially, the charge pressure supplied to the pressure balancing solenoid moves the swash plate so that the pump is at full stroke. Once the system pressure builds and opens the sequence valve, the control pressure or destroke pressure is supplied to the swash plate control to destroke the main pump away from full stroke to stabilize the system pressure at the max system pressure governed by the system control or sequence valve.
For example, the system pressure may be 5200 psi but the system control valve is adjusted to reduce this maximum system pressure to 4200 psi as the adjusted maximum system pressure. The adjusted pressure is at a high pressure and is supplied to a pressure reducer so that a reduced control pressure is usable in the pressure balancing solenoid in conjunction with the lower pressure generated by the charge pump wherein the relative magnitudes of the control pressure and charge pressure vary the swash plate position. This reduced control pressure is fed to the swash plate control and balances with the charge pressure from the charge pump. Preferably, the control pressure destrokes the pump so as to operate as a destroke pressure. The swash plate control therefore has two balanced pressures which find equilibrium by movement of a spring-biased piston in the swash plate control which piston then mechanically moves the swash plate to control the output displacement of the main pump.
As the swash plate moves, it lowers the pump output pressure from the main pump which thereby reduces the pressure to the motors which in turn reduces the outlet pressure of the liquid pump. Hence, by manually adjusting the system control valve by rotating the knob, the system pressure driving the motors is raised or lowered which thereby raises or lowers the outlet pressure of the liquid pump.
In this manner, the system of driving and controlling the water pumps is all hydraulic and virtually no electronic controls are required to operate the system at a set outlet pressure. While some electronics may be provided primarily for system monitoring and safety shutoff, such electronics may be omitted or disabled for various reasons and the pumping system will continue to operate. Also, this is a fast reacting system. When water valves or other process valves of the fluid distribution system are closed downstream of the liquid pumps by an operator, this dramatically stops the liquid flow yet there is no pressure surge in the system that would be caused if the pumps kept operating after the process valve was closed. This is a particular concern for positive displacement pumps which differ from centrifugal pumps.
Other objects and purposes of the invention, and variations thereof, will be apparent upon reading the following specification and inspecting the accompanying drawings.
Certain terminology will be used in the following description for convenience and reference only, and will not be limiting. For example, the words “upwardly”, “downwardly”, “rightwardly” and “leftwardly” will refer to directions in the drawings to which reference is made. The words “inwardly” and “outwardly” will refer to directions toward and away from, respectively, the geometric center of the arrangement and designated parts thereof. Said terminology will include the words specifically mentioned, derivatives thereof, and words of similar import.